The determination of angular velocity as well as linear acceleration is essential in civil airplanes, missiles, combat aircraft and the like. There are known in the art many methods and apparatuses for achieving this purposes.
Thus, it is known to employ gyroscopes for the determination of rate of rotation and linear acceleration. The use of a gyroscope for such measurement resides in the principle of spinning a symmetrical rotor at very high speed about its axis of symmetry. Consequently, there will exist a very high angular momentum about this axis and, according to Law of Conservation of Angular Momentum, the angular momentum of the rotor about the spinning axis will tend to be conserved in the event of an external rotation applied to the gyroscope.
Accordingly, as an external rotation is applied to the gyroscope, a compensating moment is applied thereto whose magnitude is a function of the applied rate of spin. In reality, angular momentum is not exactly conserved on account of frictional and other losses. Therefore, in order to achieve good results, frictional losses must be minimized and the angular momentum of the rotor should be made as large as possible. Therefore, in order for gyroscopes to be sufficiently sensitive, it is necessary for a relatively massive rotor to be spun within substantially frictionless bearings at a very high rate of spin.
Such systems are inherently expensive and subject the bearings to very high forces. This, in turn, imposes a relatively short lifespan on the gyroscope.
Consequently, in spite of the popularity of the gyroscope for measuring rates of rotation, there have been moves in recent years to employ the Coriolis effect in so-called "non-gyroscopic" inertia measuring devices. The principle of the Coriolis effect is that when a body moves linearly in a specified direction whilst, at the same time, being subjected to a rotation about an axis perpendicular to the direction of linear motion, then the linear and angular velocities combine vectorially to produce a force which is applied to the body in a direction which is mutually perpendicular both to the spin axis and the direction of linear motion. The magnitude of the resultant force, called the Coriolis force, is a function of the rate of rotation at which the body rotates and may therefore be used as a basis for its determination. Thus, if:
.omega.=the angular velocity vector of the body, PA0 v=the linear velocity vector of the body, PA0 m=the mass of the body, and PA0 F=the magnitude of the Coriolis force, then PA0 F=2 m .omega..times.v
where .omega..times.v is the vector cross product of the vectors .omega. and v.
The Gyrotron utilizes this phenomenon by employing a tuning-fork type of element rotated about its longitudinal axis. The times of the fork are subjected to a forced high frequency oscillation by means of a pair of electromagnetic drive coils. Since the forced oscillation is perpendicular to the axis of rotation of the fork, a Coriolis force will be generated along a mutually perpendicular, transverse axis, the magnitude of which force is detected by means of a pair of electromagnetic pick-up coils. Determination of the Coriolis response may be used to determine the rate of rotation of the fork about its longitudinal axis.
U.S. Pat. No. 3,839,915 discloses a turn rate sensor of the vibratory tuning fork type, as described above with respect to the Gyrotron. In such an arrangement, a rotation about an axis parallel to the times of the fork in combination with forced oscillation of the tines themselves, gives rise to a Coriolis force along a mutually perpendicular transverse axis. The system further provides for the compensation of asymmetry of the tuning fork and misalignment of the tine motions, so as to minimize errors.
However, while the prior art apparatus that utilize the Coriolis effect for determining the rate of rotation of a moving body are attractively compact, cheap and accurate, they all share the basic drawback of being capable of determining the angular velocity about one single axis only. In addition, known devices of this kind are incapable of measuring any linear acceleration. Consequently, if it is desired to measure the angular velocity components about three orthogonal axes and to determine the linear acceleration components along the same axes, three separate angular velocity sensors and three additional linear acceleration sensors are required, i.e. altogether six sensors. Whereas each of the sensors is relatively small the combination of two sets of three sensors each, is cumbersome, which may give rise to payload problems and in certain applications such as in missle war heads.
It is an object of the invention to provide an apparatus for determining the rate of rotation and the linear acceleration of a moving body embodying the advantages of apparatus based on the Coriolis effect capable of measuring angular velocity components of a moving body in two orthogonal axes. It is a further object of the present invention to provide an apparatus of the kind specified also capable of measuring the linear acceleration components in the same two orthogonal axes.